Method for manufacturing optical coupling element, optical transmission substrate, optical coupling component, coupling method, and optical interconnect system

ABSTRACT

An optical coupling structure that interfaces between optical devices mounted on a substrate and optical waveguides formed in the substrate. A manufacturing method includes preparing a wafer formed on an inorganic solid material on a dicing tape and cutting the back surface of the wafer to form substantially angled portions using a dicing blade having a point angle. The dicing tape is stripped from the wafer and the wafer is separated at the valleys between the substantially angled portions to obtain an optical coupling element. The obtained optical coupling element is a three-dimensional polyhedral light-reflecting member having a mirror surface corresponding to a surface of the wafer. The obtained optical coupling element is inserted into a trench that opens, substantially perpendicular to an optical waveguide of an optical transmission substrate, in the main surface of the optical transmission substrate to provide a structure for optical coupling with the outside.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority under 35 U.S.C. 119 from JapanesePatent Application 2009-110334, filed Apr. 30, 2009, the entire contentsof which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to optical wiring technology. Moreparticularly, it relates to a method for manufacturing an opticalcoupling element for providing an optical coupling structure thatinterfaces between optical devices mounted on a substrate and opticalwaveguides formed on the substrate.

2. Description of Related Art

In recent years, high-end server systems have introduced a technologyfor interconnected processors and cores using optical wiring to achievehigher-speed information processing. As the performance of the centralprocessing unit (CPU) of a server system increases, packaging densityand the number of CPU cores increase, thus increasing the number ofchannels of an optical data link per unit processor-core. Under suchcircumstances, development of a technology for interconnecting devices,such as processors and memories, at high speed and high density is beingrequired.

As a promising candidate of the technology for interconnecting devicesat high speed and high density, as described above, a technology forachieving a data link among chips on a printed circuit board (PCB)through optical waveguides formed on the surface of the PCB attractsattention. However, this technology has a problem in achieving theinterface between the optical waveguides formed on the board and chipson the board at high efficiency.

FIG. 14 shows a cross sectional view of an optical coupling structurefor an optical waveguide and the outside according to related art. Theoptical coupling structure 500 shown in FIG. 14 includes an electricalwiring board 502 on which electrical wiring is provided and an opticalwiring layer 506 formed on the surface of the electrical wiring board502. The optical wiring layer 506 includes a core 508 that transmits anoptical signal and clad layers 504 a and 504 b formed so as to enclosethe core 508. The optical wiring layer 506 has, in the path of the core508, an end face 512 perpendicular to the optical axis of the core 508and to the top surface of the electrical wiring board 502 and areflecting surface 510 having an inclination angle of 45° cut out. Thereflecting surface 510 and the end face 512 are formed by laser beammachining, and the reflecting surface 510 is masked with gold, aluminum,or the like by vapor deposition.

With the optical coupling structure 500 shown in FIG. 14, light thatpropagates in the core 508 travels in the core 508 in the directionindicated by the dotted-chain line, exits from the end face 512, isincident on the reflecting surface 510 at an incidence angle of 45°,where it is reflected at a right angle to the outside of the board. Thelight exiting to the outside is introduced into a receiver or the likeon the board. If a transmitter or the like is provided on the board,light exiting from the transmitter is incident on the reflecting surface510 at an incidence angle of 45°, where it is reflected at a right angleinto the core 508 through the end face 512 and propagates in the core508 reversely. In this manner, with the optical coupling structure 500shown in FIG. 14, optical devices mounted on the board, such as areceiver and a transmitter, and the optical waveguide of the board areinterfaced.

Another method for forming a reflecting surface for an opticalcommunication interface includes technology disclosed in JapaneseUnexamined Patent Application Publication No. 2001-195771. A micromirroris formed on a silicon substrate by anisotropic etching or forming ahalf-mirror by forming an optical waveguide in contact with amicromirror surface formed on a silicon substrate by anisotropic etchingand transferring the shape of the micromirror to an end face of theoptical waveguide. Furthermore, Japanese Unexamined Patent ApplicationPublication No. 2006-259590 discloses a technology for forming a 45°mirror surface by cutting a submount at an angle of 45° with respect tothe optical axis using a dicing saw with an angle of 45°.

In the optical coupling structure 500 shown in FIG. 14, the reflectingsurface 510 and the end face 512 are processed to about 50 μm to severalmillimeters in size. The reflecting surface 510 has been formed by laserbeam machining. However, the laser beam machining degrades in machiningperformance for inclined surfaces and significantly degrades inmachining performance, in particular, for minute regions. Therefore, themethod is not enough to obtain a reflecting surface with high flatness,resulting in increasing a reflection loss.

The technologies disclosed in Japanese Unexamined Patent ApplicationPublications No. 2001-195771 and No. 2006-259590 form a reflectingsurface on a silicon substrate. Accordingly, those technologies neitherform the reflecting surface in the optical wiring layer 506, as shown inFIG. 14, nor dispose a reflecting surface formed in a silicon substratein the optical wiring layer 506. In addition, with the technology of theJapanese Unexamined Patent Application Publications described above,since the reflecting surface itself is formed by being cut with a dicingsaw, it is not enough because it is difficult to obtain a reflectingsurface with high flatness, thus resulting in an increase in reflectionloss.

Thus, it has still been required to develop a technology for interfacingbetween optical waveguides formed on an optical transmission substrateand optical devices on the optical transmission substrate at highefficiency with a low reflection loss.

SUMMARY OF THE INVENTION

In accordance with one aspect of the present invention, a method formanufacturing an optical coupling element includes preparing a waferformed of an inorganic solid material on a dicing tape, cutting the backsurface of the wafer to form substantially angled portions using adicing blade having a point angle. The dicing tape is stripped from thewafer and the wafer is separated at the valleys between thesubstantially angled portions to obtain, as the optical couplingelement, a three-dimensional polyhedral light-reflecting member having amirror surface corresponding to a surface of the wafer.

In accordance with another aspect of the present invention, an opticaltransmission substrate that transmits an optical signal includes anoptical waveguide and an optical coupling unit provided in a trench thatopens in the main surface of the substrate, substantially perpendicularto the optical waveguide and in close contact with an end face of theoptical waveguide. The optical coupling unit includes athree-dimensional polyhedral light-reflecting member formed of aninorganic solid material and having a mirror surface that obliquelyintersects the optical axis of the optical waveguide to provide theoptical transmission substrate with a structure for optical couplingwith the outside.

In accordance with a further aspect of the present invention, an opticalcoupling component is inserted into a trench that opens, substantiallyperpendicular to an optical waveguide of an optical transmissionsubstrate, in the main surface of the optical transmission substrate.The optical coupling component includes a three-dimensional polyhedrallight-reflecting member formed of an inorganic solid material and havinga mirror surface configured to obliquely intersect the optical axis ofthe optical waveguide whose end face is in close contact with theoptical coupling component to provide the optical transmission substratewith a structure for optical coupling with the outside.

In accordance with a still further aspect of the present invention, amethod is provided for interfacing an optical waveguide of an opticaltransmission substrate that transmits an optical signal with theoutside. The method includes opening a trench substantiallyperpendicular to the optical waveguide in the main surface of theoptical transmission substrate and forming an optical coupling unit inthe trench and in close contact with an end face of the opticalwaveguide. The optical coupling unit includes a three-dimensionalpolyhedral light-reflecting member formed of an inorganic solid materialand having a mirror surface that obliquely intersects the optical axisof the optical waveguide to provide the optical transmission substratewith a structure for optical coupling with the outside.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the configuration of an optical printed circuit boardaccording to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view of the optical printed circuit boardaccording to a first embodiment of the present invention before anoptical coupling component 110 is fitted therein.

FIG. 3 shows a method for manufacturing a light-reflecting member of theoptical coupling component according to an embodiment of the presentinvention, as well as the cross-sectional structures in the individualprocesses.

FIG. 4(A) is a schematic diagram of the back surface of a silicon wafer;and FIG. 4(B) is a perspective view of a light-reflecting member cut outfrom the silicon wafer.

FIG. 5 shows an example of a method for forming a mirror surface havingconcave portions, as well as cross-sectional structures in theindividual processes.

FIG. 6 shows a method for forming a mirror surface M having concaveportions according to an embodiment that uses the liquid etching agent.

FIG. 7 shows an optical interconnect system including the opticalprinted circuit board according to the first embodiment of the presentinvention.

FIG. 8 shows the configurations of optical printed circuit boardsaccording to other embodiments of the present invention.

FIG. 9 is a diagram showing the configuration of an optical printedcircuit board according to still another embodiment of the presentinvention.

FIG. 10(A) is a picture showing the appearance of a diced silicon wafer;FIG. 10(B) is a diagram showing a profile obtained by measuring theheights of the front and back surfaces of the cut portion of the wafer;and FIG. 10(C) is a diagram showing a cutout rod-like silicon mirror.

FIG. 11(A) shows an optical microscopic image of silicon mirrors; andFIG. 11(B) shows a microscopic image of an end of the silicon mirror.

FIG. 12(A) is a schematic diagram showing the state of a silicon mirrorelectrostatically attracted to the tips of support plates of anelectrostatic holding device; and FIG. 12(B) is a picture of the same.

FIG. 13(A) is a picture of the cross section of a manufactured opticalcoupling structure; and FIG. 13(B) is a picture of the board taken fromthe top thereof substantially perpendicular thereto.

FIG. 14 is a cross sectional view showing an optical coupling structurefor an optical waveguide and the outside according to related art.

While embodiments of the present invention are described hereinbelowwith reference to the attached drawings, the present invention is notlimited to the embodiments shown in the attached drawings. Note that theattached drawings are not always scaled down or up according to scale.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In accordance with the present invention, an optical coupling structurecapable of achieving a high-efficiency interface with a low reflectionloss is achieved by using, as the light reflecting member, athree-dimensional polyhedral member having a mirror surfacecorresponding to the front surface of a wafer formed of an inorganicsolid material, the polyhedral member being obtained by cutting the backsurface of the wafer with a dicing blade and by separating it, thusarriving at the present invention.

Specifically, according to the present invention, a method formanufacturing an optical coupling element inserted into a trench thatopens, substantially perpendicular to an optical waveguide of an opticaltransmission substrate, in the main surface of the optical transmissionsubstrate provides the optical transmission substrate with a structurefor optical coupling with the outside.

According to the manufacturing method a wafer is formed of an inorganicsolid material is mounted on a dicing tape. The back surface of thewafer is cut to form substantially angled portions using a dicing bladehaving a point angle. The dicing tape is stripped from the wafer and thewafer is separated at the valleys between the substantially angledportions to obtain, as the optical coupling element, a three-dimensionalpolyhedral light-reflecting member having a mirror surface correspondingto a surface of the wafer.

With the configuration described above, the surface of the wafer, whichis polished into a mirror surface with high flatness bychemical-mechanical polishing or the like and is not subjected tomachining using a dicing blade or the like, can be used as the mirrorsurface of the light-reflecting member. This allows high reflectionefficiency. The wafer surface can be provided with a metal layer or acoating in advance, so the reflection efficiency can easily be improved.Furthermore, since the obtained light-reflecting member is processedwith high accuracy by the dicing blade, it is advantageous also inaligning the mirror surface to a predetermined inclination angle withrespect to the optical axis of the optical waveguide.

According to the present invention, an optical coupling componentincluding the three-dimensional polyhedral light-reflecting member andhaving a shape to be fitted in a trench having an inner wall surfacethat is substantially perpendicular to the substrate main surface can beformed. Furthermore, according to the present invention, concaveportions can be formed at positions on the surface of the wafercorresponding to the channels of the optical waveguide in advance byetching the surface of the wafer. The above configuration allows aconcave pattern that is in accurate alignment with the cutting patternof the back surface of the wafer to be formed on the surface of thewafer. Thus, it can be said that this manufacturing method isadvantageous in terms of forming a mirror surface having concaveportions corresponding to the cores of the optical waveguide. Accordingto the present invention, the optical coupling unit can have, incorrespondence with the channels of the optical waveguide, a verticaloptical waveguide structure formed of a material having a lightrefractive index higher than or equal to the light refractive index ofthe material of the cores of the optical waveguide. The above verticaloptical waveguide structure can include a portion that is in contactwith the light-reflecting member of the optical coupling unit and havinga light refractive index higher than the material of the cores. In thiscase, a light confining effect can be obtained even in the vicinity ofthe reflecting portion, thus satisfactorily reducing a loss ininterfacing.

According to the present invention, the wafer can be cut to form thesubstantially angled portions at a pitch interval shorter than or equalto the length of the short side of the base of the trench that opens inthe main surface of the optical transmission substrate. Furthermore, thelight-reflecting member can be configured such that the mirror surfaceis inclined at substantially 45° with respect to the outer wall of theoptical coupling component that is substantially perpendicular to theoptical axis of the optical waveguide. The point angle of the dicingblade can be set at substantially 90°.

An optical transmission substrate transmits an optical signal. Theoptical transmission substrate includes an optical coupling unit in atrench that opens in the main surface of the substrate substantiallyperpendicular to the optical waveguide. The optical coupling unit isprovided with a three-dimensional polyhedral light-reflecting memberformed of an inorganic solid material and having a mirror surface thatobliquely intersects the optical axis of the optical waveguide in closecontact with an end face of the optical waveguide. The optical couplingunit provides the optical transmission substrate with a structure foroptical coupling with the outside.

With the above configuration of the present invention, the reflectionsurface is provided by the mirror surface of the three-dimensionalpolyhedral light-reflecting member that is processed with high accuracyindependently from the optical transmission substrate. Accordingly, theoptical coupling structure can efficiently interface between the opticalwaveguide of the optical transmission substrate and the outside with alow reflection loss.

According to the present invention, the surface cut out from the waferas the mirror surface can be used as the light-reflecting member of thethree-dimensional polyhedral light-reflecting member. Since the surfaceof the wafer can be polished into the mirror surface bychemical-mechanical polishing, significantly high flatness can beachieved. The above configuration allows the high-flatness wafer surfacecan be used as the mirror surface, thus allowing high reflectionefficiency to be achieved. Furthermore, since the wafer surface can beprovided with a metal layer or a coating in advance, it is advantageousin improving the reflection efficiency.

According to the present invention, the trench that opens in thesubstrate main surface substantially perpendicular to the opticalwaveguide can have an inner wall surface that is substantiallyperpendicular to the substrate main surface. The optical coupling unitcan be formed in such a manner that an optical coupling component formedin a shape to be fitted in the trench is inserted into the trench. Withthe above configuration, the light-reflecting member is modularized intoa shape that is to be fitted in the trench that opens in the opticaltransmission substrate, which makes it easy to align the optical axis ofthe optical waveguide and the mirror surface when forming the opticalcoupling structure.

Furthermore, the mirror surface can be provided as a surface of thethree-dimensional polyhedron and may have concave portions correspondingto the channels of the optical waveguide. The above configuration allowsthe concave portions formed on the mirror surface to function as concavemirrors, thus satisfactorily reducing the spread of light reflected bythe mirror surface.

The three-dimensional polyhedron may be a triangular prism. Lightemitted from the end face of the optical waveguide is reflected in adirection substantially perpendicular to the substrate main surface. Incontrast, light that has been incident on the substrate main body from adirection perpendicular thereto is reflected to the end face of theoptical waveguide. Furthermore, according to the present invention, aplurality of surfaces, except the mirror surface, of thelight-reflecting member may be in face-contact with the inner wallsurfaces of the trench, and the mirror surface may be a side surfaceexcept the plurality of surfaces that are in face contact.

According to the present invention, there is provided an opticalcoupling component including a three-dimensional polyhedrallight-reflecting member formed of an inorganic solid material andproviding the optical coupling structure. The optical coupling componentcan further include a positioning member for positioning the level ofthe mirror surface of the light-reflecting member with respect to theoptical axis of the optical waveguide.

Furthermore, according to the present invention, a method is providedfor interfacing an optical waveguide of an optical transmissionsubstrate that transmits an optical signal with the outside. First, atrench is formed, substantially perpendicular to the optical waveguide,in the main surface of the optical transmission substrate. An opticalcoupling unit including a three-dimensional polyhedral light-reflectingmember formed of an inorganic solid material and having a mirror surfacethat obliquely intersects the optical axis of the optical waveguide isprovided in the trench and in close contact with an end face of theoptical waveguide. The above configuration allows the optical waveguideformed in the optical transmission substrate and the outside to easilybe interfaced with each other.

According to the present invention, there is provided an opticalinterconnect system including the optical transmission substrate and anoptical device disposed on the optical transmission substrate. In theoptical interconnect system, the optical device on the substrate and theoptical waveguide are connected through the mirror surface of thethree-dimensional polyhedral light-reflecting member formed of aninorganic solid material. The above configuration can satisfactorilyreduce a loss that can occur during optical data transmission, therebyachieve an optical data link among optical devices on the opticaltransmission substrate. Furthermore, if the mirror surface has concaveportions corresponding to the cores of the optical waveguide, the spreadof light that transmits optical signals is reduced, thus satisfactorilyreducing crosstalk among the cores and a decrease in signal strength.

Optical printed circuit boards in which an optical wiring layer isformed on an electrical wiring board according to embodiments of thepresent invention are described hereinbelow as examples of the opticaltransmission substrate.

FIG. 1 shows the configuration of an optical printed circuit board 100according to a first embodiment of the present present invention. FIG.1(A) is a top view of the optical printed circuit board 100; and FIG.1(B) is a cross-sectional view of the optical printed circuit board 100taken along line X shown in FIG. 1(A). The optical printed circuit board100 shown in FIG. 1 includes an electrical wiring board 102 on whichelectrical wiring is provided and an optical wiring layer 106 formed onthe electrical wiring board 102 so as to cover all or part thereof. Theelectrical wiring board 102 is what is called a multilayer printedcircuit board (PCB) that transmits electric signals and electric powerto electronic devices mounted on the optical printed circuit board 100.

The optical wiring layer 106 includes a core 108 that constitutes thechannel of an optical waveguide and clad layers 104 a and 104 b thatencloses the core 108. As shown in FIG. 1(A), the optical wiring layer106 can include a plurality of cores 108. If the optical wiring layer106 includes the plurality of cores 108, the clad layer 104 can beconfigured as a single clad layer that encloses the plurality of cores108.

The optical wiring layer 106 including the cores 108 and the clad layer104 is formed of a photosensitive organic polymeric material, such aspolyimide resin, polyamide resin, polyether resin, or epoxy resin, by,for example, photolithography, on which optical wiring with a desiredcircuit pattern is defined. The cores 108 and the clad layer 104 areformed of materials with different refractive indexes.

Here, in the optical wiring layer 106, a portion defined, including agroup of cores 108 indicated by the broken lines in FIG. 1(A), isreferred to as a parallel optical waveguide 106 a. The parallel opticalwaveguide 106 a has a width L. The optical wiring layer 106 has a trench(groove) that is open, substantially perpendicular to the paralleloptical waveguide 106 a and vertically to the top surface of theelectrical wiring board 102, in the path of the parallel opticalwaveguide 106 a. In the optical printed circuit board 100 of thisembodiment, an optical coupling component 110 is fitted in the trench.The optical coupling component 110 includes a mirror surface M thatintersects the optical axes of the individual cores 108 of the paralleloptical waveguide 106 a at an inclination angle of substantially 45°.Thus, an optical coupling structure for interfacing the parallel opticalwaveguide 106 a with the outside is provided.

With the optical printed circuit board 100 shown in FIG. 1, if areceiver or the like is disposed on the optical printed circuit board100, light that is propagated in the cores 108 travels along an opticalpath B indicated by the dotted-chain line. Specifically, the light thatis propagated in the individual cores 108 is incident on the mirrorsurface M at an incidence angle of 45°, where it is reflected at a rightangle with respect to the optical axis of the parallel optical waveguide106 a and exits vertically from the top surface of the board 100 towardthe outside. The light that exits to the outside enters the receiver orthe like disposed on the optical printed circuit board 100 and isconverted to an electric signal by a photoelectric transducer.

If a transmitter or the like is disposed on the optical printed circuitboard 100, light that is vertically incident on the board 100 from thetransmitter is incident on the mirror surface M at an incidence angle of45°, where it is reflected at a right angle, is incident on the cores108, and is propagated in the cores 108 in the reverse direction. Inthis manner, with the optical printed circuit board 100, the opticalcoupling structure provided by inserting the optical coupling component110 into the trench allows an optical device disposed on the board, suchas a receiver or a transmitter, and the parallel optical waveguide 106 aof the board 100 to be interfaced with each other.

FIG. 2 shows a cross-sectional view of the optical printed circuit board100 before the optical coupling component 110 is fitted therein. Thecross-sectional view shown in FIG. 2 also corresponds to the line Xshown in FIG. 1(A), as in FIG. 1(B). As shown in FIG. 2, the opticalprinted circuit board 100 has a trench 120 that opens in the surface ofthe board 100. The trench 120 includes, as an inner wall surface, afacetted end face F that is perpendicular to the parallel opticalwaveguide 106 a and vertical to the optical axes of the cores 108 and tothe top surface of the board 100. It is preferable that the other innerwall surfaces of the trench 120 be also formed vertically with respectto the main surface of the board 100 in view of forming a preferableoptical coupling structure.

Although not particularly limited, the size of the trench 120 can be setat about 35 μm to 1 mm in the lateral direction of the cross section andat about several millimeters to several centimeters in width(corresponding to the width L of the parallel optical waveguide 106 a)in correspondence with the array of the cores 108 included in theparallel optical waveguide 106 a. The depth of the trench 120 can be setat a depth corresponding to the thickness of the optical wiring layer106 and the depth of the cores 108 of the parallel optical waveguide 106a. In the embodiment shown in FIGS. 1 and 2, the trench 120 isconfigured such that the base thereof corresponds to the surface of theelectrical wiring board 102. However, the trench 120 may be formed at adepth, for example, in the middle of the optical wiring layer 106depending on the size of a light-reflecting member 114, to be describedlater, that provides the mirror surface M. The trench 120 is formed onthe surface of the optical printed circuit board 100 by, for example,laser beam machining.

The optical coupling component 110 to be inserted into the trench 120includes the light-reflecting member 114 that provides the mirrorsurface M, a connecting member 116, and a support plate 112. Theconnecting member 116 connects the cores 108, the mirror surface M, andthe support plate 112 together to provide a medium that propagateslight. The connecting member 116 attaches to the light-reflecting member114 and has an outer wall surface C opposed to the above facetted endface F to fit the optical coupling component 110 in the trench 120. Thesupport plate 112 provides a medium for propagating light together withthe connecting member 116 and, in addition, functions as a positioningmember that locates the optical coupling component 110 so that it isinserted to a predetermined depth at which the mirror surface Mcorresponds to the level of the cores 108 and is stopped. The connectingmember 116 and the support plate 112 are formed of a light-transmissiveorganic polymeric material, as described above. When the opticalcoupling component 110 is fitted, a transparent resin adhesive isinjected into the gap between the trench 120 and the optical couplingcomponent 110 so that the optical coupling component 110 is secured inthe trench 120.

The light-reflecting member 114 has a three-dimensional polyhedralshape, whose one surface serves as the mirror surface M. In a preferableembodiment, the light-reflecting member 114 can be substantially anisosceles right-angled triangular prism, as shown in FIG. 2. In thiscase, one side surface of the triangular prism including the base of theisosceles right-angled triangular cross section provides the mirrorsurface M. However, the three-dimensional polyhedron is not limited tothe isosceles right-angled triangular prism but may be anythree-dimensional polyhedron having a trapezoidal or a scalenetriangular cross section and whose mirror surface M reflects light at anangle of 90° when disposed in the trench. The following description ismade on the assumption that the light-reflecting member 114 has anisosceles right-angled triangular shape.

In the optical coupling component 110, the mirror surface M is bonded tothe connecting member 116 at an angle of substantially 45° with respectto the outer wall surface C and is adjusted so as to obliquely intersectthe optical axes of the cores 108 of the parallel optical waveguide 106a at an inclination angle of substantially 45° when inserted into thetrench 120. The length of the triangular prism of the light-reflectingmember 114 preferably corresponds to the width of the trench 120 formedacross the parallel optical waveguide 106 a, and two sides of the crosssection preferably correspond to the length of the short side of thebase of the trench 120.

The mirror surface M of the light-reflecting member 114 can be flat overthe surface, or alternatively, have spherical or aspherical concaveportions corresponding to the individual cores 108 of the paralleloptical waveguide 106 a. If the mirror surface M of the light-reflectingmember 114 has concave portions, light reflected by the mirror surface Mis condensed, so that the spread of the light that transmits opticalsignals is satisfactorily reduced. The mirror surface M of thelight-reflecting member 114 may be provided with a metal layer, such asgold or chromium, or a coating, such as a dielectric material, inadvance.

The light-reflecting member 114 according to the embodiment of thepresent invention may be formed of a monocrystal silicon wafer. However,a material for forming the light-reflecting member 114 is not limited tothe silicon wafer described above and may be a wafer-shaped crystallineor noncrystalline inorganic solid material having high processability,such as another silicon wafer, a GaAs wafer or another compoundsemiconductor wafer, an oxide monocrystal wafer, or a metal plate.

Referring now to FIGS. 3 and 4, a method for manufacturing an opticalcoupling component according to an embodiment of the present inventionwill be described. FIGS. 3(A) to 3(D) are diagrams showing a method formanufacturing a light-reflecting member of the optical couplingcomponent according to the embodiment of the present invention, as wellas cross-sectional structures in the individual processes. Here, a casein which the light-reflecting member 114 is formed of a silicon waferwill be described by way of example.

Referring to FIG. 3(A), according to this manufacturing method, asilicon wafer 130 is mounted on a ring frame (not shown), with a dicingtape 140 therebetween. Here, the silicon wafer 130 is mounted on thedicing tape 140 so as to protect the surface of the silicon wafer 130,which used as the mirror surface M in the optical coupling component110. The silicon wafer 130 prepared is reduced in thickness into adesired thickness by, for example, polishing the back surface in advanceand has, for example, a thin wafer shape with a thickness of about 30 μmto 1 mm.

In the case where concave portions are formed on the mirror surface M ofthe light-reflecting member 114, the surface of the prepared siliconwafer 130 is provided with the concave portions in advance. In the casewhere a metal layer or a coating is formed on the mirror surface M ofthe light-reflecting member 114, the surface of the prepared siliconwafer 130 is provided with the metal layer by plating or vapordeposition or is provided with the coating, such as a dielectricmaterial, in advance.

Referring to FIG. 3(B), according to the manufacturing method, the backsurface of the silicon wafer 130 is then cut to form angled portions ata predetermined pitch interval P using a dicing blade 142 having a pointangle of substantially 90°. This pitch interval P corresponds to thelength of the opposite side of the isosceles right-angled triangle ofthe cross section of the light-reflecting member 114 and is set at alength of, for example, 50 μm to 1.4 mm depending on the shape of theparallel optical waveguide 106 a on which the optical coupling component110 is mounted. Also for the direction perpendicular to theangled-portion cutting direction, the silicon wafer 130 is cut atappropriate intervals corresponding to the width L of the paralleloptical waveguide 106 a by blade dicing or Stealth dicing before orafter the step shown in FIG. 3(B).

FIG. 4(A) schematically shows the back surface of the silicon wafer 130subjected to dicing. As shown in FIG. 4, the silicon wafer 130 is cut toform angled portions at the predetermined pitch interval P and is cut ata predetermined pitch L corresponding to the width L of the paralleloptical waveguide 106 a in a direction D perpendicular to theangled-portion cutting direction.

Referring to FIG. 3(C), according to the manufacturing method, next,ultraviolet light is radiated from the back of the dicing tape 140 todecrease the adhesiveness of the dicing tape 140, thereby stripping offthe dicing tape 140 from the surface of the silicon wafer 130.

Referring to FIG. 3(D), according to the manufacturing method, next, theangled portions cut from the silicon wafer 130 are separated to obtainthe plurality of light-reflecting members 114 having the shape of anisosceles right-angled triangular prism. At that time, thelight-reflecting members 114 can be separated from on another bypressing a razor edge against the valleys of the angled portions. If anexpanding dicing tape 140 is used, the silicon wafer 130 may be dividedafter dicing under the action of the dicing tape 140 expanded in thedirection of the wafer surface.

FIG. 4(B) shows a perspective view of the light-reflecting member 114cut out from the silicon wafer 130. As shown in 4(B), the obtainedlight-reflecting member 114 has the shape of substantially an isoscelesright-angled triangular prism and has the mirror surface M having thelength L and the width P, with the opposite side O of the vertex of thebase (cross section) of the triangular prism as a short side. Since thesurface of the silicon wafer 130 is normally polished into a mirrorsurface by chemical-mechanical polishing (CMP), significantly highflatness can be achieved. Since the manufacturing method according tothe embodiment of the present invention provides, as the mirror surfaceM, a wafer surface that is not mechanically processed by a dicing bladeetc., high reflection efficiency can be achieved. Furthermore, since thewafer surface can be provided with a metal layer or a coating inadvance, higher reflection efficiency can be achieved.

The obtained light-reflecting member 114 is processed with high accuracyinto a substantially isosceles right-angled triangular prism with a sizespecified by the pitch interval P and the pitch interval L set for thedicing. This makes it advantageous also in aligning the mirror surface Mto a predetermined inclination angle with respect to the optical axis ofthe optical waveguide.

After the light-reflecting member 114 shown in FIG. 4(B) is obtained,the light-reflecting member 114 is disposed in an appropriate metalmold. The orientation of the mirror surface M is adjusted using, forexample, an electrostatic holding device, the above-mentioned organicpolymeric material is injected into the metal mold to embed thelight-reflecting member 114 therein into the shape shown in FIGS. 1 and2. As shown in FIG. 2, the modularized configuration of the opticalcoupling component 110 having a shape to be fitted in the trench 120formed in the optical printed circuit board 100 facilitates thealignment of the optical axis of the optical waveguide and the mirrorsurface M during optical coupling.

Referring now to FIG. 5, a method for forming the mirror surface Mhaving concave portions is described. FIGS. 5(A) to 5(D) are diagramsshowing an example of the method for forming the mirror surface M havingconcave portions, as well as cross-sectional structures in theindividual processes. FIG. 5 shows a cut surface provided in thedownstream process shown in FIG. 3(B) ais indicated by a broken line.The forming method shown in FIG. 5 is performed before the silicon wafer130 is mounted on the dicing tape 140 in FIG. 3(A). The processes shownin FIG. 5 are performed in alignment with substantially the angledpattern cut in the process shown in FIG. 3(B).

Referring to FIG. 5(A), according to the forming method, first, apositive resist film 240 is applied onto the surface of a silicon wafer230, on which a grayscale mask 250 is disposed. The grayscale mask 250includes a glass substrate 254 and a thin film 252 that is patterned onthe glass substrate 254. The thin film 252 is patterned so as to formconcaves at the positions of the mirror surfaces M intersecting theoptical axes of the individual cores 108 of the parallel opticalwaveguide 106 a when the light-reflecting member 114 is disposed in thetrench 120.

Referring to FIG. 5(B), according to the forming method, the positiveresist film 240 is exposed with light through the grayscale mask 250 fordevelopment. The intensity of exposure light is controlled according tothe pattern of the thin film 252 of the grayscale mask 250, so that thepositive resist film 240 is exposed to light into a shape correspondingto the concave portions. When the exposed resist film 240 is developed,portions exposed to light are removed to form concave portions 240 a inthe resist film 240 to become the state shown in FIG. 5(B).

Referring to FIG. 5(C), according to the forming method, the siliconwafer 230 is then subjected to isotropic dry etching together with thedeveloped resist film 240 by dry etching using plasma etching gas. Bythe dry etching, the concave portions 240 a formed in the resist film240 is transferred to the silicon wafer 230 to form concave portions 230a on the surface of the silicon wafer 230.

Referring to FIG. 5(D), according to the forming method, the remainingresist film 240 is then removed. A metal layer of chromium or gold isevaporated onto the surface of the silicon wafer 230 on which theconcave portions 230 a are formed or a coating is formed by spin coatingor the like to form a reflection improved layer 232. After the formingmethod shown in FIG. 5 is performed, the silicon wafer 230 is mounted onthe dicing tape 140 in alignment with the pattern of the concaveportions 230 a in FIG. 3(A), and the processes shown in FIGS. 3(B) to3(D) are performed.

The method for forming the mirror surface M having the concave portionsis not limited to the embodiment shown in FIG. 5. In another embodiment,for example, a negative resist film may be used instead of the positiveresist film 240. In yet another embodiment, concave portions, as shownin FIG. 5(B), may be formed on the resist film 240 by pressing a metalmold having desired concave portions, instead of the grayscale mask 250,against the resist film 240.

In still another embodiment, desired concave portions can be formed onthe surface of the silicon wafer 230 by forming openings at locations ofthe resist film 240 corresponding to the centers of individual concaveportions and performing anisotropic wet etching using a liquid etchingagent through the openings. FIG. 6 is a diagram showing a method forforming the mirror surface M having concave portions according to theembodiment that uses the liquid etching agent. FIG. 6(A) shows a topview of the resist film 240; and FIG. 6(B) shows a cross-sectional viewthereof.

Referring to FIGS. 6(A) and 6(B), according to the forming method of theother embodiment, openings 242 are formed at the locations correspondingto the concave portions of the resist film 240 by lithography. Theopenings 242 are formed at substantially the centers of regionscorresponding to the mirror-surface reflecting members at apredetermined pitch interval S. The pitch interval S corresponds to thepitch interval between the cores 108 included in the parallel opticalwaveguide 106 a. By performing anisotropic wet etching on the surface ofthe silicon wafer 230 using the etching mask shown in FIGS. 6(A) and6(B), desired concave portions can be formed on the surface.

The concave portions formed on the mirror surface M by theabove-described forming method function as concave mirrors tosatisfactorily reduce the spread of light reflected by the mirrorsurface M. As described above, the method for manufacturing the opticalcoupling component according to the embodiment of the present inventionallows the wafer surface to be used as the mirror surface M. Theportions formed on the wafer surface, such as concave portions, can beformed in accurate alignment with the cutting pattern of the backsurface of the wafer. Thus, it can be said that this manufacturingmethod is advantageous in terms of forming a mirror surface havingconcave portions corresponding to the cores of the optical waveguide.

Referring to FIG. 7, an optical interconnect system using the opticalprinted circuit board according to the first embodiment of the presentinvention will be described hereinbelow. FIG. 7 shows an opticalinterconnect system 150 including the optical printed circuit board 102according to the first embodiment of the present invention. The opticalinterconnect system 150 shown in FIG. 7 includes the electrical wiringboard 102 and the parallel optical waveguide 106 a defined on theoptical wiring layer 106. The electrical wiring board 102 has an opticaltransmitter chip module 160 and an optical receiver chip module 180mounted thereon. The parallel optical waveguide 106 a has opticalcoupling components 110 a and 110 b fitted in two trenches formed atboth end portions, respectively.

The optical transmitter chip module 160 includes a carrier 162 mountedon the electrical wiring board 102, with solder bumps 164 therebetween,and an LDD (laser diode driver) array IC 170 mounted on the carrier 162,with solder bumps 168 therebetween. The carrier 162 has an opticalcomponent 166 including a lens array and a VCSEL (vertical cavitysurface emitting laser) array. The VCSEL array is driven by the LDDARRAY IC 170 to introduce optical signals of the individual channelsinto the cores 108 in the parallel optical waveguide 106 a through theoptical coupling component 110 a.

The optical receiver chip module 180 includes a carrier 182 mounted onthe electrical wiring board 102, with solder bumps therebetween, and aTIA (transimpedance-amplifier) array IC 186 mounted on the carrier 182,with solder bumps therebetween. The carrier 182 has an optical component184 including a lens array and a PD (photo diode) array. When opticalsignals through the individual channels are introduced into theindividual channels of the PD array through the optical couplingcomponent 110 b, the TIA array IC 186 converts the optical signals inputfrom the PD array to electric signals.

In this manner, in the optical interconnect system 150 shown in FIG. 7,optical devices mounted on the board 102, such as the opticaltransmitter chip module 160 and the optical receiver chip module 180,are interfaced with the parallel optical waveguide 106 a using theoptical coupling components 110 a and 110 b to achieve an optical datalink between the optical devices. As has been described, the mirrorsurface M of the optical coupling component 110 according to theembodiment of the present invention has high flatness, thereby allowinga loss that could be generated during optical data transmission to bereduced satisfactorily. Furthermore, if the mirror surface M has theconcave portions corresponding to the cores 108 of the parallel opticalwaveguide 106 a, the spread of light that transmits signals can besatisfactorily reduced, thus satisfactorily reducing crosstalk betweenthe cores 108 and a decrease in the intensity of the signals.

Referring now to FIGS. 8 and 9, optical coupling structures according toother embodiments of the present invention are described. FIG. 8 showsthe configurations of optical printed circuit boards according to otherembodiments of the present invention. Since the optical printed circuitboards 300, 320, and 340 shown in FIG. 8 have configurations similar tothat shown in FIG. 1, differences will be mainly described hereinbelow.The cross-sectional views shown in FIG. 8 are taken along a line thatvertically crosses the cores of the optical waveguides, as is thecross-sectional view shown in FIG. 1.

FIG. 8(A) is a cross-sectional view of the optical printed circuit board300 according to a second embodiment of the present invention. Theoptical printed circuit board 300 shown in FIG. 8(A) includes anelectrical wiring board 302 and an optical wiring layer 306 constitutedof cores 308 and a clad layer 304.

In the embodiment shown in FIG. 8(A), an optical coupling structure forinterfacing between the parallel optical waveguide and the outside isnot achieved by a modularized optical coupling component as in the firstembodiment. Instead, in the embodiment shown in FIG. 8(A), alight-reflecting member 314 similar to that of the first embodiment isdisposed in a trench that opens in the path of the parallel opticalwaveguide, and the interior of the trench is filled with a transparentpolymeric resin material 316 or the like to constitute an opticalcoupling component 310. The light-reflecting member 314 is fitted in thetrench so that the mirror surface M of the light-reflecting member 314obliquely intersects the optical axes of the cores 308 of the paralleloptical waveguide at an inclination angle of substantially 45° and issecured with the polymeric resin material 316.

Also in the optical printed circuit board 300 shown in FIG. 8(A), lightthat has traveled in the individual cores 308 toward the end face isreflected by the mirror surface M at a right angle to the optical axisof the parallel optical waveguide and exits vertically from the topsurface of the board 300 toward the outside. In contrast, light that hasbeen incident on the board 300 perpendicular thereto is reflected at aright angle by the mirror surface M into the cores 308 and is propagatedin the reverse direction. In this manner, with the optical printedcircuit board 300 shown in FIG. 8(A), external optical devices, such asa receiver or a transmitter, disposed on the board 300 and the paralleloptical waveguide of the board 300 are interfaced with each other usingthe optical coupling structure provided by the light-reflecting member314 secured in the trench with the polymeric resin material 316. Theconfiguration shown in FIG. 8(A) can be used in the case where there isno need to modularize the light-reflecting member 314 as an opticalcoupling component.

FIG. 8(B) is a cross-sectional view of the optical printed circuit board320 according to a third embodiment of the present invention. In theoptical printed circuit board 320 shown in FIG. 8(B), an optical wiringlayer 326 is constituted of cores 328 a, 328 b, and 328 c arrayed inlayers and a clad layer 324.

An optical coupling component 330 includes a light-reflecting member 334having a mirror surface M of a size corresponding to the array of themultilayered cores 328. Thus, also with a multilayered opticalwaveguide, as shown in FIG. 8(B), optical signals transmitted through aplurality of channels of the cores 328 are reflected substantially at aright angle by the mirror surface M and are introduced into opticaldevices mounted on the board 320. Alternatively, optical signals emittedfrom optical devices mounted on the board 320 are reflectedsubstantially at a right angle by the mirror surface M and areintroduced into the individual cores 328.

FIG. 8(C) is a cross-sectional view of the optical printed circuit board340 according to a fourth embodiment of the present invention. Theoptical printed circuit board 340 shown in FIG. 8(C) further includes anupper substrate layer 350 formed on a first optical wiring layer 346. Atrench is formed vertically from the surface of the optical printedcircuit board 340 through the upper substrate layer 350 and the firstoptical wiring layer 346 to reach a lower substrate 342. An opticalcoupling component 360 including a light-reflecting member 364 isembedded in the trench.

The optical coupling component 360 shown in FIG. 8(C) includes a supportsubstrate 368, a light-reflecting member 364 and a second optical wiringlayer 374 secured on the support substrate 368, and a connecting member366 that bonds the light-reflecting member 364 and the second opticalwiring layer 374. The second optical wiring layer 374 includes aplurality of cores 372 corresponding to the individual cores 348 of theparallel optical waveguide of the first optical wiring layer 346 formedin the board 340. A clad layer 370 of the second optical wiring layer374 is formed to enclose the cores 372. In the embodiment shown in FIG.8(C), an end of the support substrate 368 is in contact with the base ofthe trench to serve as a positioning member for positioning the level ofthe mirror surface M.

With the optical coupling component 360 shown in FIG. 8(C), theinterface between the optical waveguide of the second optical wiringlayer 374 formed in the substrate and the outside is achieved. While theoptical path length increases with the thickness of the upper substratelayer 350, the intervals corresponding to the thickness of the uppersubstrate layer 350 are coupled by the second optical wiring layer 374.This can satisfactorily prevent a decrease in coupling efficiency due tolight diffusion caused from an increase in optical path length.Moreover, since the second optical wiring layer 374 can be formed in theboard 340, an increase in the temperature of the optical waveguideduring the manufacturing process can be reduced as compared with a casein which the optical wiring layer is formed on the surface of the board.This improves the thermal resistance of the optical printed circuitboard 340.

FIG. 9 is a diagram showing the configuration of an optical printedcircuit board according to still another embodiment of the presentinvention. FIG. 9(A) is a cross-sectional view of an optical printedcircuit board 380 according to a fifth embodiment of the presentinvention. The optical printed circuit board 380 shown in FIG. 9(A)includes an electrical wiring board 382 and an optical wiring layer 386constituted of cores 388 having a square cross section and a clad layer384. The optical printed circuit board 380 shown in FIG. 9(A) is anembodiment in which a trench that opens to the surface of the board 380is formed in correspondence with one square cross-section core of theoptical waveguide.

In the embodiment shown in FIG. 9(A), an optical coupling structure forinterfacing between the optical waveguide and the outside is provided byan optical coupling component 390 including a light-reflecting member394 disposed in the trench, as in the second embodiment. The trench hasa depth corresponding to the level of the lower ends of the cores 388and a width equal to the widths of the square cross sections of thecores 388 of the optical waveguide and opens in a square shape as viewedfrom the front surface. The light-reflecting member 394 disposed in thetrench has a length corresponding to the width of the trench and a sizecorresponding to the cores 388. The light-reflecting member 394 isfitted in the trench so that the mirror surface thereof obliquelyintersects the optical axes of the cores 388 of the optical waveguide atan inclination angle of substantially 45° and is secured with apolymeric resin material 396. In this embodiment, an optical waveguideconfiguration can be formed also in the vertical direction (verticaloptical waveguide configuration) by setting the light refractive indexof the polymeric resin material 396 injected into the trench equal to orhigher than that of the cores 388 of the optical waveguide.

FIG. 9(B) shows a modification of the fifth embodiment of the presentinvention. In the modification shown in FIG. 9(B), the polymeric resinmaterial 396 of the optical coupling component 390 is constituted of twoportions 396 a and 396 b having different refractive indexes. In thismodification, the refractive index of the polymeric resin portion 396 athat is in contact with the light-reflecting member 394 should be equalto, or preferably, slightly higher than that of the cores 388 of theoptical waveguide formed in the board 380. In other words, it ispreferable that the conditions of the refractive indexes, n2≦n3≦n2 ²/n1and n2≦n4≦n2 ²/n1, be satisfied, where n1 is the refractive index of theclad layer 384, n2 is the refractive index of the cores 388, and n3 andn4 are refractive indexes of the polymeric resin portions 396 a and 396b, respectively.

In particular, setting the refractive index n3 of the portion 396 awhose cross section is an isosceles right-angled triangle, which is incontact with the light-reflecting member 394, higher than the refractiveindex n2 of the cores 384 provides a light confining effect, thussatisfactorily reducing a loss in the optical coupling component 390.The light confining effect occurs even in the vicinity of the reflectingportion, The above description is made, with reference to FIG. 9(A),about the case where the light-reflecting member 394 is fitted in thetrench and is secured with the polymeric resin material 396 to therebyform the optical coupling component 390. However, also in the fifthembodiment having the vertical optical waveguide configuration, theoptical coupling component may be modularized into a shape that isfitted in the trench, as in the first embodiment. In this case, thevertical optical waveguide configuration may also be formed incorrespondence with the individual cores in the parallel opticalwaveguide.

With the optical printed circuit board according to the embodiments ofthe present invention described above, the surface of the wafer, whichis polished into a mirror surface by CMP processing, can be used as themirror surface M that allows interfacing with the outside withoutmechanical processing using a dicing blade or the like. This allows amirror surface having high flatness and high reflectance to be easilyobtained as compared with the method for forming an inclined reflectingsurface by laser beam machining of the related art and can achieve highoptical coupling efficiency. Furthermore, since the mirror surface M caneasily be provided with a metal layer or a coating in advance, thereflectance can easily be improved.

The optical coupling structure according to an embodiment of the presentinvention is described more specifically using an example. However, thepresent invention is not limited to a specific example.

EXAMPLE (MANUFACTURING LIGHT-REFLECTING MEMBER)

A 1500 Å of gold or chromium metal layer was evaporated on the surfaceof a silicon wafer (made by Enatek, Ltd.) with a thickness of about 70μm and a diameter of 4 inches.

The prepared silicon wafer was bonded on a dicing tape of an ultravioletoff type, with the surface up, and was mounted on a ring frame.Subsequently, the silicon wafer was cut at a pitch interval P of 100 μmfrom the back using a diamond blade having a 90° point angle (made byDISCO Corporation) to form angled portions in a pattern shown, inoutline, in FIG. 4(A) and was further cut at a pitch interval L of 5 mmin the direction perpendicular to the angled portions using a dicingblade. Subsequently, ultraviolet light was radiated from the back of thedicing tape to strip off the dicing tape from the surface of the siliconwafer.

FIG. 10(A) is a picture showing the appearance of the diced siliconwafer. FIG. 10(A) shows a cut portion at substantially the center of thesilicon wafer. FIG. 10(B) is a diagram showing the appearance of the cutportion of the back surface of the wafer (cut surface) observed by aprofile measurement microscope (made by Keyence Corporation, typenumber: VK-8550) and a profile (referred to H in the drawing) obtainedby measuring the height of the back surface of the wafer. As shown inFIG. 10(B), a profile showing good angled portions was obtained. FIG.10(C) shows a single rod-like silicon mirror that is obtained by cuttingout a necessary length of silicon wafer in the direction perpendicularto the first dicing in the bonded state after the measurement in FIG.10(B).

Subsequently, a razor was pressed against the individual valleys betweenthe angled portions formed on the back surface of the wafer inregistration therewith to separate the angled portions into a pluralityof substantially isosceles right-angled triangular prism siliconmirrors. FIG. 11(A) shows an optical microscopic image of the obtainedsilicon mirrors 400. FIG. 11(B) shows a microscopic image of an end ofthe obtained silicon mirror 400. As shown in FIG. 11(B), it wasconfirmed that the silicon mirror 400 has the shape of a substantiallyisosceles right-angled triangular prism having preferable cut surfaces.

(Forming Optical Coupling Structure)

The obtained silicon mirror 400 was handled using an electrostaticholding device shown in FIG. 12(A) under a microscope and was fitted ina trench formed in a 100-μm thick resin layer, prepared as dummy, on thesilicon substrate. FIG. 12(A) is a diagram showing, in outline, theelectrostatic holding device used for handling the silicon mirror. Asshown in FIG. 12(A), high voltage was applied between two holding plates410 a and 410 b, that is, two metal plate electrodes coated with aninsulator (polyimide), to hold the silicon mirror 400 in a contactmanner at the tips of the holding plates 410 a and 410 b using anelectrostatic attracting force. FIG. 12(B) is a picture showing thesilicon mirror 400 electrostatically attracted to the tips of theelectrostatic holding device.

Subsequently, a transparent ultraviolet cure resin 420 (made of KyoritsuChemical & Co. Ltd.) was injected into the trench to harden the resin byradiating light, thereby securing the silicon mirror 400 fitted in thetrench in the trench. FIG. 13(A) is a picture of the cross section of anoptical coupling structure formed when the silicon mirror 400 is securedin the trench with the transparent resin 420. FIG. 13(A) shows thesilicon mirror 400 secured in the trench with the resin 420. FIG. 13(B)shows a picture of the board taken from the top thereof substantiallyperpendicular thereto while radiating light from the side of the board.As shown in FIG. 13(B), light radiated from the side of the board wasreflected by the silicon mirror 400.

The example shows that an optical coupling structure that interfaceswith the outside can be configured by using a silicon mirror cut from awafer as a light-reflecting member, with the surface of the wafer onwhich a metal layer is formed as a mirror surface, and disposing thesilicon mirror in a trench provided in a light transmitting layer.

Although the present invention has been described with reference tospecific embodiments, it is to be understood that the invention is notlimited to the foregoing embodiments. Modifications, other embodiments,additions, changes, and deletions may be made within the scope in whichthose skilled in the art can consider and such modifications areincluded in the scope of the invention as defined in the followingclaims.

1. A method for manufacturing an optical coupling element, the methodcomprising the steps of: preparing a wafer formed of an inorganic solidmaterial on a dicing tape; cutting the back surface of the wafer to formsubstantially angled portions using a dicing blade having a point angle;stripping the dicing tape from the wafer; and separating the wafer atthe valleys between the substantially angled portions to obtain, as theoptical coupling element, a three-dimensional polyhedrallight-reflecting member having a mirror surface corresponding to asurface of the wafer.
 2. The method according to claim 1, furthercomprising the step of forming, as the optical coupling element, anoptical coupling component including the obtained three-dimensionalpolyhedral light-reflecting member and having an inner wall surface thatis substantially perpendicular to the substrate main surface.
 3. Themethod according to claim 2, further comprising the step of etching thesurface of the wafer before the step of preparing the wafer to formconcave portions at positions corresponding to the channels of theoptical waveguide.
 4. The method according to claim 3, wherein thecutting step includes cutting the wafer to form the substantially angledportions at a pitch interval shorter than or equal to the length of theshort side of the base of the trench that opens in the main surface ofthe optical transmission substrate.
 5. The method according to claim 4,wherein the forming step includes configuring the mirror surface to beinclined at substantially 45° with respect to the outer wall of theoptical coupling component that is substantially perpendicular to theoptical axis of the optical waveguide.
 6. An optical transmissionsubstrate that transmits an optical signal, the optical transmissionsubstrate having a main surface and comprising: an optical waveguide;and an optical coupling unit provided in a trench that opens in the mainsurface of the substrate, substantially perpendicular to the opticalwaveguide and in close contact with an end face of the opticalwaveguide; said optical coupling unit including a three-dimensionalpolyhedral light-reflecting member formed of an inorganic solid materialand having a mirror surface that obliquely intersects the optical axisof the optical waveguide to provide the optical transmission substratewith a structure for optical coupling with the outside.
 7. The opticaltransmission substrate according to claim 6, wherein: the trench has aninner wall surface that is substantially perpendicular to the substratemain surface; and the optical coupling unit is formed in such a mannerthat an optical coupling component formed in a shape to be fitted in thetrench is inserted into the trench.
 8. The optical transmissionsubstrate according to claim 7, wherein the mirror surface has concaveportions corresponding to the channels of the optical waveguide.
 9. Theoptical transmission substrate according to claim 8, wherein the opticalcoupling unit has, in correspondence with the channels of the opticalwaveguide, a vertical optical waveguide structure formed of a materialhaving a light refractive index higher than or equal to the lightrefractive index of the material of the cores of the optical waveguide.10. The optical transmission substrate according to claim 6, wherein thethree-dimensional polyhedron is a triangular prism, and the mirrorsurface reflects light emitted from the end face of the opticalwaveguide in a direction intersecting the substrate main surface orreflects incident light through the substrate main surface toward theend face of the optical waveguide.
 11. The optical transmissionsubstrate according to claim 6, wherein: a plurality of surfaces, otherthan the mirror surface, of the light-reflecting member are inface-contact with the inner wall surfaces of the trench; and the mirrorsurface is a side surface other than the plurality of surfaces that arein face contact.
 12. The optical transmission substrate according toclaim 6, wherein: the optical coupling unit was formed by inserting anoptical coupling component formed in a shape to be fitted in the trenchinto the trench and includes a three-dimensional polyhedrallight-reflecting member formed of an inorganic solid material and havinga mirror surface that obliquely intersects the optical axis of theoptical waveguide to provide the optical transmission substrate with astructure for optical coupling with the outside; the light-reflectingmember is configured such that the three-dimensional polyhedron is atriangular prism that is cut off from the wafer, with a surface of thewafer served as the mirror surface, a plurality of surfaces, except themirror surface is in face-contact with the inner wall surfaces of thetrench; and the mirror surface (i) is provided as a surface of thethree-dimensional polyhedron, (ii) has concave portions corresponding tothe channels of the optical waveguide and (iii) reflects light emittedfrom the end face of the optical waveguide in a direction intersectingthe substrate main surface or reflects incident light through thesubstrate main surface toward the end face of the optical waveguide. 13.An optical coupling component inserted into a trench that opens,substantially perpendicular to an optical waveguide of an opticaltransmission substrate, in the main surface of the optical transmissionsubstrate, the optical coupling component comprising: athree-dimensional polyhedral light-reflecting member formed of aninorganic solid material and having a mirror surface configured toobliquely intersect the optical axis of the optical waveguide whose endface is in close contact with the optical coupling component to providethe optical transmission substrate with a structure for optical couplingwith the outside.
 14. The optical coupling component according to claim13, wherein the mirror surface is provided as a surface of thethree-dimensional polyhedron and has concave portions corresponding tothe channels of the optical waveguide.
 15. The optical couplingcomponent according to claim 14, further comprising a positioning memberfor positioning the level of the mirror surface with respect to theoptical axis of the optical waveguide.
 16. A method for interfacing anoptical waveguide of an optical transmission substrate that transmits anoptical signal with the outside, the method comprising the steps of:opening a trench, substantially perpendicular to the optical waveguide,in the main surface of the optical transmission substrate; and formingan optical coupling unit in the trench and in close contact with an endface of the optical waveguide, said optical coupling unit including athree-dimensional polyhedral light-reflecting member formed of aninorganic solid material and having a mirror surface that obliquelyintersects the optical axis of the optical waveguide to provide theoptical transmission substrate with a structure for optical couplingwith the outside.